The invention relates to a ring-gap nozzle for distributing a fluid medium over a plate, comprising an axial channel passing through the plate the said channel being covered by a cap so as to leave a ring gap between the cap and the plate, whilst the cap is held by means of a connecting member which passes coaxially through the channel and is attached to a clamp which is mounted at the start of the channel, in the direction of flow of the medium, thus forming an annular flow space, in which the medium flowing in the channel region axially is deflected in a deflection space and flows out radially through the ring gap.
Ring-gap nozzles of this kind are advantageously used in the bottom plate of a fluidised bed apparatus and serve to distribute the flowing medium which is to be used for fluidisation of the bed. The ring-gap nozzles are arranged on the surface of the plate at a spacing from one another and are intended to distribute and conduct the medium so as to form a cushion of medium along the surface to prevent the particles of product which are to be treated in the fluidised bed from coming into contact with the heated plate. This cushion thus prevents the product from being damaged or from burning or baking on to the surface of the bottom plate.
However, the ring-gap nozzles known hitherto do not always meet these requirements. Particularly in cases where the medium contains particles of solids, these particles may be deposited in the flow chamber of the nozzle as they pass through and thus from agglomerations on the walls which obstruct the flow of medium or, eventually, block the nozzle completely. The desired flow along the plate and the fluidisation of the bed alter and become inadequate in the course of time, and the entire fluidised bed apparatus has to be shut down in order to restore the nozzles to normal operation. In the case of aggressive or abrasive particles, the profiles of the nozzles which conduct the current of medium are also affected, and sometimes damaged to such an extent that the apparatus has to be put out of action to repair the nozzles. In a number of known cases, it has even been necessary to replace the entire bottom plate of the apparatus.